In recent years, engines in which a variable valve timing device configured to control valve timings of an intake valve and an exhaust valve in correspondence to a driving state of an engine is mounted for high output, low-fuel consumption and low exhaust gas have been increasingly used. In this type of engines, an engine has been known in which a hydraulic pressure to the variable valve timing device is controlled with an oil control valve unit arranged at a front side of a cylinder head (for example, refer to Patent Document 1). The oil controlled with the oil control valve unit is supplied to an advance chamber and a retard chamber of the variable valve timing device and a rotation phase of a camshaft relative to a crankshaft is changed, so that the valve timing is adjusted.    Patent Document 1: Japanese Patent No. 5345448B
In the meantime, a vehicle body frame is mounted to the engine so that the engine is covered with the vehicle body frame. When the oil control valve unit is mounted to an outer surface of the engine, the oil control valve unit may interfere with the vehicle body frame upon mounting of the vehicle body frame, depending on a mounting position of the oil control valve unit. In the engine disclosed in Patent Document 1, the oil control valve unit is mounted to the front side of the cylinder head, so that interference between the vehicle body frame and the oil control valve unit is suppressed. However, the mounting position of the oil control valve unit is limited due to a shape of the vehicle body frame.